This proposal seeks a competing continuation of R01 HL52555-09. Mitogen-activated protein kinases (MAPKs) serve diverse functions in biological signaling relays, including cascades for cardiac development, hypertrophy, and the transition to heart failure. The Applicant's investigations are directed at decoding the biological function of proximal MAPKs in the myocardium mMAP kinase kinase kinases (MAP3Ks) and MAP kinase kinase kinase kinases (MAP4Ks) that fall close to signal generation in the hierarchy of signaling events. Transforming growth factor beta-activated kinase-1 (TAK1, MAP3K7) and its activation are especially well-suited for such studies. Work performed during our prior period of support has established that TAK1 modulates the AMP-activated protein kinase (AMPK) energy sensor pathway for glycogen storage cardiomyopathy and Wolff-Parkinson-White syndrome. Also, we recently identified a novel feed-forward circuit that amplifies cardiac apoptotic signals, reciprocally coupling levels of TRF2, a telomere-capping protein, to TAK1 via MAP4K4 (hematopoietic progenitor kinase/germinal cell kinase-like kinase, HGK). Alternative splicing of HGK exon 16 results in two transcdpts that differ by the inclusion or exclusion of an SH3 domain and are co-expressed at equal levels in myocardium. Interesting, in acute cell culture studies, we found only the short form of HGK leads to myocyte apoptosis. Decimation of Baylor's vivarium by Tropical Storm Allison in June 2001 set back our expected progress towards the conditional deletion of TAK1 and HGK by roughly two years. However, we now have germline transmission or, minimally, chimeric mice for all three "floxed" alleles required in this project. We propose: (1) To determine the critical function(s) of endogenous TAK1, using conditional dominant-negative and loss-of-function mutations. (2) To study the essential function(s) of endogenous HGK, a TAKl-activating kinase, using a conditional loss-of-function mutation and conditional deletion of the alternatively spliced SH3 domain.